1. Field of the Invention
The present invention relates to a structure of a solid state image sensor, and particularly to a solid state image sensor in which smear reduction is effected to an optimum extent.
2. Description of the Related Art
Typically, a color image sensor is configured to have three rows of CCD (Charge Coupled Device) linear image sensors arranged therein in parallel with one another, each row including a CCD and having a function of transferring electric charges, and to form a color filter including, for example, a red color filter, a green color filter and a blue color filter, and corresponding to a color different from other colors on each of photodiodes of each of the three rows of linear image sensors.
FIG. 1 illustrates the entire configuration of an exemplified color image sensor having the aforementioned construction. The image sensor includes: two rows of photodiodes 121, 141, each photodiode of the row having a color filter (not shown) thereon consisting of one of a red (R) color filter, a green (G) color filter and a blue (B) color filter; and control gates 122, 142 for retrieving signal charges photo-electrically converted within a photodiode from the photodiode for transfer of the signal charges to charge transfer registers 126, 146. Thus, signal charges Q1, Q2, Q3, Q4 . . . are retrieved and supplied to the charge transfer registers 126, 146 (denoted by a white arrow in the figure). Readout pulses xcfx86TG1, xcfx86TG2 and xcfx86TG3 (bus lines are not shown for simplification) for retrieving signal charges are applied to the control gates 122, 142. The charge transfer registers 126, 146 each include two-phase CCD registers, and signals xcfx861 and xcfx862 are applied to the charge transfer registers 126 and 146, respectively (pulse lines are not shown). The signal charges transferred through the charge transfer registers 126, 146 are transferred to a floating diffusion region. The signal charges transferred to the floating diffusion region are converted to a signal voltage through a charge detector. The signal voltage obtained by conversion of the signal charges is outputted as a color signal from an output circuit 103 including an analog circuit such as a source follower, inverter or the like to the outside.
FIG. 2 is a plan view of a color image sensor having CCD linear image sensors, each linear image sensor including a single row of photodiodes and corresponding to an individual color, and configured to retrieve electric charges only from one side of the row of photodiodes. The configuration of CCD linear image sensor other than the aforementioned configuration is the same as that shown in FIG. 1.
In recent years, need for high resolution and high integration density enhances reduction in pixel size. For this reason, a solid state image sensor incorporating a plurality of CCD linear image sensors, each linear image sensor having two rows of photodiodes, which are alternately arranged at an interval of half the pixel size in a direction of the row, potentially introduces a light beam incident on the photodiode in one row through an opening for the photodiode into another photodiode in the other row. When the aforementioned phenomenon occurs, a difference between the amounts of signal charges from different rows of photodiodes is caused even if the same amount of a light beam is irradiated on each of the two rows of photodiodes.
FIG. 3 is a plan view of a conventional solid state image sensor. FIG. 4 is an enlarged cross sectional view of the solid state image sensor, taken along the line Ixe2x80x94I of FIG. 3 and corresponding to a portion, enclosed by a dashed circle line, of the drawing of FIG. 3. FIG. 4 illustrates an enlarged view of a photodiode for photo-electrically converting a light beam incident thereon and a charge transfer register for transferring electric charges generated within the photodiode by photo-electric conversion. Though not clearly shown in the plan view of the entire solid state image sensor of FIG. 3, a boundary between photodiodes in a longitudinal direction (i.e., a direction of the row of photodiodes) includes boron ions implanted thereinto so that electric charges produced within a certain photodiode by photo-electric conversion are not able to enter a photodiode adjacent to the certain photodiode. In the figure, a color filter is also omitted for simplification.
As shown in FIG. 4, when viewing the paper from a direction vertical to the paper, a light beam 62 incoming through an opening 61 corresponding to a photodiode 1 on the left should typically be photo-electrically converted within the photodiode 1 (denoted by a dashed line) on the left. However, the light beam 62 incident on the opening 61 from a direction inclined relative to the normal to the opening 61 is reflected by an interconnect line 10 serving also as a light shielding material and then passes through an interlayer insulation film 36 between through holes 5, and finally enters the photodiode 1 on the right, producing a difference between the amounts of electric charges generated within the photodiodes on the adjacent rows of photodiodes.
FIG. 5 is an enlarged cross sectional view of the solid state image sensor, taken along the line IIxe2x80x94II of FIG. 3 and corresponding to a portion, enclosed by a dashed circle line, of the drawing of FIG. 3. As shown in FIG. 5, a second polysilicon electrode 11 used to retrieve signal charges and the interconnect line 10 are connected to each other through an opening 13 provided in the interlayer insulation film 36. However, the interconnect line 10 is only filled within the opening 13 and is not configured to penetrate the interlayer insulation film 36 in the form of a one-piece conductive plate in a direction of the row. Accordingly, the light beam 62 incident on the photodiode 1 from a direction inclined relative to the normal to the photodiode 1 enters also a first polysilicon electrode 2 as a charge transfer electrode through the interlayer insulation film 36 between the openings 13. In this case, the light beam entering the first polysilicon electrode 2 probably permeates through defects or the like in the charge transfer electrode and then impinges on a charge transfer channel beneath the charge transfer electrode.
A solid state image sensor incorporating a plurality of CCD linear image sensors, each linear image sensor having a single row, corresponding to one color, of photodiodes, is shown in FIGS. 6 through 8. FIG. 6 is a plan view of the solid state image sensor including a plurality of CCD linear image sensors, each linear image sensor having a single row of photodiodes, and FIG. 7 is an enlarged cross sectional view of the solid state image sensor, taken along the line Ixe2x80x94I of FIG. 6 and corresponding to a portion, enclosed by a dashed circle line, of the drawing of FIG. 6, and FIG. 8 is an enlarged cross sectional view of the solid state image sensor, taken along the line IIxe2x80x94II of FIG. 6. In the solid state image sensor of the type described above, as shown in FIGS. 7, 8, a light beam 62 incoming from a direction inclined relative to the normal to a photodiode 1 on the left is reflected by an interconnect line 10 serving also as a light shielding material and passes through an interlayer insulation film 36 between through holes 6, and finally enters the photodiode 1 on the right, producing electric charges within the photodiode 1 on the right. The electric charge thus produced causes a difference between the amounts of electric charges generated within the photodiodes in the rows of photodiodes corresponding to the individual CCD linear image sensors, causing a difference between the amplitudes of output signals, i.e., causing smear.
The present invention is directed to a solid state image sensor incorporating a plurality of CCD linear image sensors, each linear image sensor having a single row or two rows of photodiodes, and being capable of reducing a difference between outputs from the plurality of linear image sensors and thereby reducing smear.
A solid state image sensor of the present invention includes: a linear image sensor having at least one row of photodiodes; a photodiode array formed such that the linear image sensor constitutes a plurality of linear image sensors, and the plurality of linear image sensors are arranged side by side; an insulation film covering the photodiode array; and a light shielding conductive film formed to penetrate the insulation film in a direction of thickness of the insulation film and partition the plurality of linear image sensors into individual linear image sensors, the light shielding conductive film serving as a light shielding film.
The solid state image sensor of the present invention further includes a charge transfer register disposed beside the at least one row of photodiodes and corresponding to the at least one row of photodiodes, in which the light shielding conductive film serves as a wall to separate the at least one row of photodiodes and the charge transfer register from each other.
The solid state image sensor of the present invention is further constructed such that the plurality of linear image sensors arranged in the photodiode array are provided to correspond to individual colors to be displayed.